CA1261915A - Fast response, high rate, gas diffusion electrode and method of making same - Google Patents
Fast response, high rate, gas diffusion electrode and method of making sameInfo
- Publication number
- CA1261915A CA1261915A CA000489373A CA489373A CA1261915A CA 1261915 A CA1261915 A CA 1261915A CA 000489373 A CA000489373 A CA 000489373A CA 489373 A CA489373 A CA 489373A CA 1261915 A CA1261915 A CA 1261915A
- Authority
- CA
- Canada
- Prior art keywords
- layer
- oxygen cathode
- particles
- active
- wetproofing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/90—Selection of catalytic material
- H01M4/9008—Organic or organo-metallic compounds
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/96—Carbon-based electrodes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Abstract
ABSTRACT OF THE DISCLOSURE
Disclosed are gas fed, porous electrodes capable of steady, high current density operation for practical periods of service, e.g. as oxygen cathodes in metal-air batteries. The subject electrodes feature at least two bonded composite layers, one of which is a form-stable, conductive wetproofing layer while the other is an unusually thin active layer containing active carbon particles predominantly between about 2 and about 20 micrometers and having a high internal surface area, e.g. a B.E.T. surface area of over 1000 m2/gram. A simple and highly successful method of preparing such electrodes is also disclosed, which avoids the necessity of separately forming and handling the thin active layer.
Disclosed are gas fed, porous electrodes capable of steady, high current density operation for practical periods of service, e.g. as oxygen cathodes in metal-air batteries. The subject electrodes feature at least two bonded composite layers, one of which is a form-stable, conductive wetproofing layer while the other is an unusually thin active layer containing active carbon particles predominantly between about 2 and about 20 micrometers and having a high internal surface area, e.g. a B.E.T. surface area of over 1000 m2/gram. A simple and highly successful method of preparing such electrodes is also disclosed, which avoids the necessity of separately forming and handling the thin active layer.
Description
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FAST ~ES~01~SE, HI~H RATEf GAS DIFFUSION ~LECTRO~E
AN~ METHOD OF MAKING SAME
Field of the Invention This invention relates to gas diffusion electrodes for use in electrolytic devices. More particularly, it is directed toward oxygen-containing gas fed, porous electrodes capable of high current density operation with good durability; for example, for service as oxygen or air cathodes in metal-air batteries.
Background of the Invention Fuel cells and metal-air batteries have been known for many years. However, comJnercial exploitation has been : ~ slower than expected due to their generally bulky structures and the difficulties encountered in attaining adequate ~power densities and~reasonabl~ sustained performance. Accordingly, much effort has been expended in developing more compact~cell~:designs and more efficient electrodes for service in the harsh chemical envi~ronments :, :
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g~L5 ~ 2 --represented by the acid or alkaline electrolytes used therein.
Porous composite electrodes containing various electroconductive and catalytic particles have often received consideration for service as oxygen cathodes in such batteries and fuel cells. Representative cathodes of this character are described for example, in U.S. Patents 3,385,780; 3,462,307; 3,553,022; and 3,668,014.
Although considerable progress has already been made in adapting such porous composite electrodes for use in electrochemical devices, the difficult problem of achieving and maintaining a controlled balance in permeability to both the liquid electrolyte and the oxygen containing gas has led to premature failures, such as blistering and delamination, under more demanding service conditions. For example, in metal-air batteries having cell potentials of about 2 volts, available porous, carbon based oxygen cathodes have not heretofore been capable oE sustained performance at high current densities (i.e. substantially above about 400 milliamps per sq. cm.) for much more than a full hour at best. One of the most common causes of oxygen cathode failure is believed to be flooding of the porous cathode structure by electrolyte, but attainable current density can also be reduced by excessive gas percolation therethrough and/or depletion of catalytic activity therein.
Ob~ects of the Invention A primary object of our invention is the provision of porous, composite oxygen cathodes which will perform at high curren~t densities continuously Eor at least several hours in a metal-air battery having a cell potential of about 2 volts or more. A corollary object is to increase ,:~
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the resistance of said cathode to flooding or structural failures, without causing poor initial wetting by electrolyte or sluggish response upon activation.
Another object is to provide such oxyyen catnodes which will operate satisfactoril~ when fed with either oxygen or air.
Secondary objects are to provide such cathodes which are resistant to percolation of gas therethrough, and to protect the catalysts used therein from inactivation or deterioration via the cell environment. Further ob]ects will become apparent from the detailed disclosures which follow.
Summary of the Invention In line with the above objects, the oxygen cathode oE
this invention comprises: a form-stable, electrically conductive, wetproofing layer composed essentially of a heat sintered, intimately consolidated mixture of carbon black and particulate hydrophobic polymeric binder derived predominantly from tetrafluoroethylene, having at least one anisometric reinforcing material incorporated therein; andr directly adhered to one surface of said wetproofing layer, an active layer having a thickness between about O.U3 and about 0.10 millimeter and composed essentially of a mixture of catalyzed particles of an active carbon predominantly of a size between about ~2 and about 20 micrometers (and preferably about 5 to about 10 micrometers) and having a Brunauer-Emmet-Teller surface area of over about lOOm2/gram and particles of a polymer of tetrafluoroethylene.
; Ideally, the oxygen cathode is prepared by a simple and economical process comprising:
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(a~ dispersing carbon black and particles of a hydrophobic pol~meric binder in an alconolic liquid, optionally with the further addition of a minor proportion of fine, short-chopped fibers, to form a well mixed particulate suspension;
(b) removing most of the alcoholic li~uid from said suspension by filtering, centrifuging, evaporation or other liquid separation techniques to leave a mud-like, damp-solids mass of well mixed carbon black and hydrophobic binder particles, optionally with a minor content of said fibers;
(c) forming said damp-solids mass into a dry, form-stable wetproofing layer by application of heat and pressure, optionally while incorporating a layer lS of fine mesh material therein;
(d) heating the dry, form-stable wetproofing layer from step (c) to a temperature above about 325C
while applying pressure thereto, thereoy causing the hydrophobic binder particles to sinter and bond with other particulate matter in said layer;
(e) forming a well mixed dispersion in alconolic liquid of particles of a polymer of tetrafluoroethylene and precatalyzed particles of active carbon having a B.E.T. surface area of over about 1000 m2/gram and predominantly ranging between about 2 and about 20 micrometers in siæe;
(f) subjecting said well mixed dispersion from step (e) to filtration using the sintered form-stable : wetproofing layer from step (d) as the filter medium to deposit over one face of said layer a thin coating of well mixed particles of sa:id catalyzed active carbon and said polymer of tetrafluoroethylene amounting to about 2 to about 6 milligrams of said well mixed particles per square centimeter of said face; and .
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(g) drying said coating in place by application of heat and pressure, thereby forming said oxygen cathode having an active la~er having a thickness of between about 0.03 and about OolO millimeter bonded to said form-stable wetproofing layer.
In one especially preferred embodiment of the invention, a fine gauge mesh or gauze is embedded in tne wetproofing layer as an "anisometric~ reinforcing material. As defined herein an ~anisometric" mesh is one wherein the individual elements of the mesh are anisometric whether or not the mesh pattern itself is essentially symmetrical. Although this mesh or gauze may be fabricated of any tough and sufficientl~ inert stabilizing material, corrosion resistant metal or other electrically conductive material is ideal since such mesh will also function as a current distributor. A very thin expanded metal sheet can be used in similar manner instead of a metal mesh or gauze.
Descri~tion of the Invention The success of the present invention in suppl1ing oxygen cathodes which are sufficiently resistant to electrolyte flooding or other breakdowns to perform in metal-air batteries for more than several hours at high current densities results primarily from the use of an unusually thin active layer of simple composition which provides both controlled permeability and balanced hydrophobicity. Thus, said active layer is not over about 0.1 millimeter in thickness and is composed essentially of an intimate mixture of precatalyzed particles of active ; carbon predominantly (i.e. at least about 55~ by weight~
within a particle size range of about 2 to about 20 :,.
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9 ~ 5 (preferably about 5 to about 10) micrometers and having a s.E.T. surEace area above about 1000 m2/gram and a particulate tetraEluoroeth~lene polymer.
The addition of fugitive pore formers, such as sodium carbonate or ammonium benzoate~ is unnecessary and is preferably avoided in the compositions used to forln the active layers of our oxygen cathodes, since the balanced permeability desired is readily achieved and controlled consistently using the above described particulate mixtures. The precatalyzed particles of active carbon may contain between about 5 and about 2~ of a catalyst effective in promoting reduction of oxygen. Among the wide number of active catalysts known to be suitable are platinum and palladium blacks and other platinum group metals and compounds, as well as silver, copper, cobalt and other metals. One type of catalyst which is particularly preferred in the present invention comprises macrocyclic organic compounds of cobalt, such as cobalt tetramethoxyphenylporphyrin. In order, to optimize its activity, this type of catalyst should be heat treated in a nitrogen atmosphere after being adsorbed on the active carbon. For example, excellent results are obtained by heating said cobalt macrocyclic in tnis manner for about 1-3 hours at about 7~0 to 90~C. ~e~ardless of the particular catalyst employed the weight proportion of catalyzed active carbon to tetrafluoroethylene (T~E) polymer should be between about 7 to 3 and about 9 to 1.
Using such simple composite mixtures to fabricate our active layers, controlled hydrophobicity and evenly : 30 balanced permea~ility are obtained particularly when the thickness of the active layer in the subject cathodes is between about 0.05 and about 0.08 millimeters. Such active layers are so thin and fragile as to discourage handling thereof as separate layers or sheets in fabricating ., 9~
electrodes of practical sizes. Accordingly, a vital corollary factor in the practical realization OL durable oxygen cathodes for high energy density service in accordance with the present invention is the provision of a S sturdy, form-stable wetprooEing layer to which said unusually thin active layer is adhered.
This wet-proofing layer is electrically conductive and is usually substantiall~ thicker than said active layer.
In addition to the intimate mixtures of carbon black and tetrafluoroethylene binder particles used in its formation, it should be further strengthened by includin~ at least one anisometric reinforciny material therein and by heat sintering under pressure. Thus, said wetproofing la~er is preferably above about 0.1 millimeters in thickness. Also, the carbon black employed therein should have a particle size between 50 and about 3000 Angstroms and preferabl~
will be a highly conductive grade of carbon black such as an acet~lene black. Most acetylene blacks average between about 300 and about S00 Angstroms in size. The preferred particulate polymer for use therewith is polytetrafluoroethylene (commercially available from DuPont under the ~T~FLON" trademark). The anisometric reinforcing material can comprise short, chopped fibers of fine denier with L/D ratio of at least lOj and/or one or more layers of fine gauge mesh or gauze material. Particularly suitable are carbon or graphite fibers from about 1 to about 10 millimeters in length and about 5 to 100 micrometers in diameter, as well as mesh materials about S0 to about 200 micrometers thick, particularly closel~ woven metallic mesh materials which greatly improve current distribution in the finished electrode. For example, metallic meshes having between about 10 and about 20 individual wires per centimeter across both warp and fill directions are ideal.
The proportions in which the various components are ::, .
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incorporated in the wetproofing la~er may be varied considerabl~ as long as a sturd~, form-stable electrically conductive layer is produced. Thus, the weight proportion of carbon black to tetrafluoroethylene binder particles should lie between about 3 to 2 and a~out 4 to 1, while the fibers used as reinforcement material should amount to between about 3% and about 25% of the combined weight of the carbon black and binder. ~einforcing mesn materials will usually constitute 10 to 25% by volume of the wetproofing layer. However, on a weight basis, the preferred electrically conductive metallic wire meshes may well account for over half of the total weignt of the wetproofing layer. ~etproofing layers acceptable for the needs of this invention have been disclosed in U.S. Patent . . _ . . .
4,468,362. If no mesh reinforcement is used, then the proportion of reinforcing fibers incorporated in the wet-proofing layer should be at least abc7ut 5~ of the combined weight of the carbon flack and binder.
Because of the inherent ~eakness of the unusually thin active layers per se, successful production of the finished oxygen cathode of this invention is reliably accomplisned by a unique but highly practical procedure wherein the sturdy, form-stable wetproofing layer is completely fabricated first ~including an embedded metallic mesh current distributor, if one is needed or desired therein), and, after heat sintering under pressure (e.g. 10 to 1000 psi), using said wetprooEing layer as a filter medium on which the composite particulates of which the active layer is to be formed are deposited from a well mixed dispersion in an alcoholic liquid by filtering same through said wetproofing layer. The alcoholic liquid emplo~ed to 7~
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produce said dispersion should contain at least 50% by volume of a lower alkanol, prefera~ly one containiny not more than 6 carbon atoms per moleculeO Water or other fairly volatile, i~ert polar li~uids can be used as diluents in said alcoholic liquid. The amount of said dispersion filtered through ~aid wetproofing layer should be sufficient to deposit a coating of somewhere between about 2 and about ~ milligrams per square centimeter of geometric area on the face of said wetproofing layer, depending on the exact thickness desired for the active layer being formedO
once said coating oE active layer particulates nas been deposited on said wetprooeing layer, it is only necessary to dry same thoroughly under steady compression, preferably using temperatures somewhat above 100C and pressures of between about S00 and a~out 300U psi. It is not necessary, and generally is not preferred, to heat sinter the active layer.
Although not essential to the production of a fast response, high current density oxygen cathode with good durability, it is, of course, permissible and may be desirable if the extra expense is warranted, to apply to the exposed face of the active layer of said cathodes thin coatings of additional materials, such as catalysts and/or hydrophilic substances. One exemplary surEace tredtment of this type involved application of a very thin coating of silver particles to provide special catalytic effects in the presence of hydrogen peroxide containing electrolytes, as well as improving the resistance of the oxygen cathode to percol~tion of gas therethrough into the electrolyte.
It was found that a suitable coating of silver could be formed by depositing on the exposed face of said active layer about 5 to 15 milligrams of silver particles predominantly between about 0.1 and about 1 micrometer in ., ~- .
size per sq. cm. from a liquid dispersion thereof using a filtration procedure similar to that used in forming the+active layer upon the finished wet~roofing layer.
Generally speaking the thickness of such an auxiliary outer layer may be about 20 to about 50 micrometers, and preferably is thinner than the active layer of the electrode in ~uestion.
The specific examples wnich follow are provided to illustrate the the invention in more detail and to demonstrate some of the valuable advantages obtained therefrom.
EXAM~LE A
æreparation of Fiber Reinforced ~etproofing Layer A well mixed aqueous dispersion of 70 parts by weight of acetylene carbon black (SHA~INIGANTM Black) to 30 parts by weight of particulate polytetrafl~oroethylene (TE~LONT 30 dlspersion) was filtered in a Buchner funnel, and the wet solids were wasned thoroughly wit~
isopropyl alcohol. About 4.4 grams (dry basis) of the alcohol washed mixture of PTFE and acetylene black were then dispersed in about 3S0 ml of iso~ropyl alcohol along with 0.23 grams of one-eighth inch (0.032 cm) long carbon Eibers (P~NEXTM CF 30), using an OsterizerTM blender.
The mixed solids in this alcoholic dispersion were tnen formed into a uniform, mud-like layer by filtering enouyh of said dispersion to deposit about 18 milligrams (dry basis) of said solids per sq. cm. on a separable filter medium. The resulting damp layer of solids was dried at a~out 115 C while compressing same at S00 psi, before removing said filter medium. Finally, tne dry consolidated layer having a thickness of about 0.3 mm was heated to about 325C for a few minutes under 200 psi pressure in order to sinter the PTFE particles, thereby bondiny the mixed particulates together into a form-stable, electrically conductive web or sheetO
EXAr~lPLE E~
Fiber Reinforced Wetproofing Layer (with metal mesh embedded therein) Example A was repeated except that, before compressing and drying the damp layer of solids at aDout 115C and 500 psi, a coextensive layer of woven metal wire mesh ~as placed on top o said damp layer so that it became embedded in the resulting dry consolidated layer. Said metal mesa was made of silver plated, nickel coated copper wire o~
about 0.12 mm in diameter, (with about 20 individual wires per centimeter across both the warp and fill directions), and weighed approximately 40 milligrams per square cm.
EX~PLE C
~iber-Free Wetproofing Layer (with metal mesh embedded tnerein) Example B was repeated except no fibers were included : 30 in the alcoholic dispersion oE PTFE and acetylene black.
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A ball milled and classified activated carbon having a ~.E.T. surface area of about llOOm2/g and about 60% by weight of which is in the ~article size ranye of about 2 to about 20 micrometers was impregnated with platinum b~
treatment with aqueous solutions of H3Pt(SO3)2O~ and H2O2 following a procedure much like that described in Example 1 of U.S. Patent 4,044,193, except that the proportions of reagents were adjusted to produce a catalyzed active carbon containing about 20~ platinum by weight. Tnis platinized active carbon was recovered by filtration, washing and drying at about 140C in air.
Twenty parts b~ weiyht of said platinized active carbon was thoroughly dispersed in about 300 ml of water using an Osterizerr~ blender and about an e~ual ~uantity of water containing enough "TE~LONTI~ 30 n to provide 5 parts by weight of PTFE was slowly blended therewith.
After the blended solids mixture was filtered out and washed with alcohol, it was redispersed in isopropanol to produce a suspension containing about 10 grams of the well mixed particles of platinized active carbon and PTFE per liter.
Varying amounts of this isopropanol suspension were 2S then filtered through four equal-sized square sections cut from the reinforced and heat sintered wetproofiny sneet made in EXAMPLE B hereinabove, said amounts being adjusted to coat said four sections with the following loadings of mixed particles from said suspension:
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B-l = 11.0 milligrams/cm2 B-2 = 3.4 milligrams/cm2 B-3 - 2.3 milliyrams/cm2 ~ B-4 = 1~7 milligrams/cm2 :. ".. ,.
, The resultant coated sections were then compressed at about 500 psi while heating to about 100C and finally pressed at about 3000 psi without Eurther heating to yield four finished electrode samples.
The durability of these sample electrodes for operation as oxygen cathodes in an environment simulating a metal-air batter~ was measured by the followiny standardized procedure.
The test cell was filled with 4 molar LiOH and provided with a chemicall~ inert nickel counter anoder a heater, a stirrer, a thermostat and a ~.C. po~er source.
On one side of said cell, a cathodic mount was provided to hold the sample electrodes directly facing toward said counter anode and including a separate gas compartment to the rear of said mount and a Luggin capillary for communicating between the test electrode and a standard Hg/~gO reference electrode, so that the half cell ~otential of the test electrode operating as an oxygen cathode could be tracked during the test.
The present series of tests was run at 25C using a current density of 500 milliamps per s~. cm. while circulating four times the theoretically needed ~uantity of air (puriEied of CO2) through the gas compartment behind the test electrode wi~h the following results.
SAMPLE ACTIVE LAYERTII~E OE STEADY OPE~ATION
ELECTRODETHICKNESS @500 ma/cm2 B-l 0.20 mm 10 minutes 30B-2 0.06 mm 6 hours B-3 0.04 mm 5 hours B-4 0.03 mm 3 hours , .,~
.
. . .
EXAMPL~ 2 Again using square sections cut from the reinforced wetproofing sheet of Example 3, a similar series of test electrodes were made as in Example 1 except that the active carbon was precatalyzed with cobalt tetramethoxyphenyl porphyrin in proportions of 1 part by weight of said porphyrin to 9 parts of active carbon, and then heat treated in N2 gas at about 800C for about 2 hours to produce the starting catalyzed active carbon component.
The sample electrodes were tested as oxygen cathodes as in Example 1 except at 60C, and tne results of tneir durability testing are summarized in the following table:
15 SAMPLE ACTI~ LAY~: STEADY OP~ATI~
ELECTRODæ SOLIDS LOADI~G THICK~S @$00 ma/cm2 ___ _~_________________________________ ___________________ B-5 6.6 9/crn 0.12 mm 1 hour ~-6 3.6 m9/cm~ 0.065 mm 6.5 hours B-7 3 3 mg/cm2 0.058 mm 11.5 hours Three isopropanol suspensions designated (X,Y and Z) were made as in ~xample 2, each containing the same proportions of PTFE and 10~ cobalt catalyzed active carbon particles and the only difference being that the starting active carbon particles were predominantly within much narrower size ranges. These suspensions were used to form active layer coatings each containing about 3.8 m9/cm2 of the solids mixture in said suspensions, using the filtration technique described in Examples 1 and 2 and additional s~uare sections of the same reinforced , 9~5 wetproofing sheet ~nade in ~xample B. The resulting coated sections o~ the wetproofing sheet were processed as in Example 1 to o~tain three additional test electrodes, each having an active layer thickness of about 0.07 mm. The results of testing these electrodes as oxyyen cathodes under the same conditions as in Example 2 were as follows:
SAMPLE P~E~OMINAI~T slr~A~y OP~ATIO
ELECTRODE SIZE RANGE @ 500 ma/cm2 ----______________________ B-X 2 and 10 m 7 hours B-Y 2 and 5 m 8 hours B-Z 5 and 10 m 19 hours The above illustrative examples are provided to give a more complete and detailed understanding of the practice oE
our invention and to point out presently preferred embodiments and some special advantages thereof.
Accordingly, those skilled in the art will now oe able to make various modifications in the specific conditions and employ other equivalent components to practice tnis invention, all of which variations are intended to be covered by the claims appended hereto.
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FAST ~ES~01~SE, HI~H RATEf GAS DIFFUSION ~LECTRO~E
AN~ METHOD OF MAKING SAME
Field of the Invention This invention relates to gas diffusion electrodes for use in electrolytic devices. More particularly, it is directed toward oxygen-containing gas fed, porous electrodes capable of high current density operation with good durability; for example, for service as oxygen or air cathodes in metal-air batteries.
Background of the Invention Fuel cells and metal-air batteries have been known for many years. However, comJnercial exploitation has been : ~ slower than expected due to their generally bulky structures and the difficulties encountered in attaining adequate ~power densities and~reasonabl~ sustained performance. Accordingly, much effort has been expended in developing more compact~cell~:designs and more efficient electrodes for service in the harsh chemical envi~ronments :, :
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,.
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g~L5 ~ 2 --represented by the acid or alkaline electrolytes used therein.
Porous composite electrodes containing various electroconductive and catalytic particles have often received consideration for service as oxygen cathodes in such batteries and fuel cells. Representative cathodes of this character are described for example, in U.S. Patents 3,385,780; 3,462,307; 3,553,022; and 3,668,014.
Although considerable progress has already been made in adapting such porous composite electrodes for use in electrochemical devices, the difficult problem of achieving and maintaining a controlled balance in permeability to both the liquid electrolyte and the oxygen containing gas has led to premature failures, such as blistering and delamination, under more demanding service conditions. For example, in metal-air batteries having cell potentials of about 2 volts, available porous, carbon based oxygen cathodes have not heretofore been capable oE sustained performance at high current densities (i.e. substantially above about 400 milliamps per sq. cm.) for much more than a full hour at best. One of the most common causes of oxygen cathode failure is believed to be flooding of the porous cathode structure by electrolyte, but attainable current density can also be reduced by excessive gas percolation therethrough and/or depletion of catalytic activity therein.
Ob~ects of the Invention A primary object of our invention is the provision of porous, composite oxygen cathodes which will perform at high curren~t densities continuously Eor at least several hours in a metal-air battery having a cell potential of about 2 volts or more. A corollary object is to increase ,:~
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the resistance of said cathode to flooding or structural failures, without causing poor initial wetting by electrolyte or sluggish response upon activation.
Another object is to provide such oxyyen catnodes which will operate satisfactoril~ when fed with either oxygen or air.
Secondary objects are to provide such cathodes which are resistant to percolation of gas therethrough, and to protect the catalysts used therein from inactivation or deterioration via the cell environment. Further ob]ects will become apparent from the detailed disclosures which follow.
Summary of the Invention In line with the above objects, the oxygen cathode oE
this invention comprises: a form-stable, electrically conductive, wetproofing layer composed essentially of a heat sintered, intimately consolidated mixture of carbon black and particulate hydrophobic polymeric binder derived predominantly from tetrafluoroethylene, having at least one anisometric reinforcing material incorporated therein; andr directly adhered to one surface of said wetproofing layer, an active layer having a thickness between about O.U3 and about 0.10 millimeter and composed essentially of a mixture of catalyzed particles of an active carbon predominantly of a size between about ~2 and about 20 micrometers (and preferably about 5 to about 10 micrometers) and having a Brunauer-Emmet-Teller surface area of over about lOOm2/gram and particles of a polymer of tetrafluoroethylene.
; Ideally, the oxygen cathode is prepared by a simple and economical process comprising:
, , , ~L~f~ 3~
(a~ dispersing carbon black and particles of a hydrophobic pol~meric binder in an alconolic liquid, optionally with the further addition of a minor proportion of fine, short-chopped fibers, to form a well mixed particulate suspension;
(b) removing most of the alcoholic li~uid from said suspension by filtering, centrifuging, evaporation or other liquid separation techniques to leave a mud-like, damp-solids mass of well mixed carbon black and hydrophobic binder particles, optionally with a minor content of said fibers;
(c) forming said damp-solids mass into a dry, form-stable wetproofing layer by application of heat and pressure, optionally while incorporating a layer lS of fine mesh material therein;
(d) heating the dry, form-stable wetproofing layer from step (c) to a temperature above about 325C
while applying pressure thereto, thereoy causing the hydrophobic binder particles to sinter and bond with other particulate matter in said layer;
(e) forming a well mixed dispersion in alconolic liquid of particles of a polymer of tetrafluoroethylene and precatalyzed particles of active carbon having a B.E.T. surface area of over about 1000 m2/gram and predominantly ranging between about 2 and about 20 micrometers in siæe;
(f) subjecting said well mixed dispersion from step (e) to filtration using the sintered form-stable : wetproofing layer from step (d) as the filter medium to deposit over one face of said layer a thin coating of well mixed particles of sa:id catalyzed active carbon and said polymer of tetrafluoroethylene amounting to about 2 to about 6 milligrams of said well mixed particles per square centimeter of said face; and .
, ' ':' ,:
(g) drying said coating in place by application of heat and pressure, thereby forming said oxygen cathode having an active la~er having a thickness of between about 0.03 and about OolO millimeter bonded to said form-stable wetproofing layer.
In one especially preferred embodiment of the invention, a fine gauge mesh or gauze is embedded in tne wetproofing layer as an "anisometric~ reinforcing material. As defined herein an ~anisometric" mesh is one wherein the individual elements of the mesh are anisometric whether or not the mesh pattern itself is essentially symmetrical. Although this mesh or gauze may be fabricated of any tough and sufficientl~ inert stabilizing material, corrosion resistant metal or other electrically conductive material is ideal since such mesh will also function as a current distributor. A very thin expanded metal sheet can be used in similar manner instead of a metal mesh or gauze.
Descri~tion of the Invention The success of the present invention in suppl1ing oxygen cathodes which are sufficiently resistant to electrolyte flooding or other breakdowns to perform in metal-air batteries for more than several hours at high current densities results primarily from the use of an unusually thin active layer of simple composition which provides both controlled permeability and balanced hydrophobicity. Thus, said active layer is not over about 0.1 millimeter in thickness and is composed essentially of an intimate mixture of precatalyzed particles of active ; carbon predominantly (i.e. at least about 55~ by weight~
within a particle size range of about 2 to about 20 :,.
`
9 ~ 5 (preferably about 5 to about 10) micrometers and having a s.E.T. surEace area above about 1000 m2/gram and a particulate tetraEluoroeth~lene polymer.
The addition of fugitive pore formers, such as sodium carbonate or ammonium benzoate~ is unnecessary and is preferably avoided in the compositions used to forln the active layers of our oxygen cathodes, since the balanced permeability desired is readily achieved and controlled consistently using the above described particulate mixtures. The precatalyzed particles of active carbon may contain between about 5 and about 2~ of a catalyst effective in promoting reduction of oxygen. Among the wide number of active catalysts known to be suitable are platinum and palladium blacks and other platinum group metals and compounds, as well as silver, copper, cobalt and other metals. One type of catalyst which is particularly preferred in the present invention comprises macrocyclic organic compounds of cobalt, such as cobalt tetramethoxyphenylporphyrin. In order, to optimize its activity, this type of catalyst should be heat treated in a nitrogen atmosphere after being adsorbed on the active carbon. For example, excellent results are obtained by heating said cobalt macrocyclic in tnis manner for about 1-3 hours at about 7~0 to 90~C. ~e~ardless of the particular catalyst employed the weight proportion of catalyzed active carbon to tetrafluoroethylene (T~E) polymer should be between about 7 to 3 and about 9 to 1.
Using such simple composite mixtures to fabricate our active layers, controlled hydrophobicity and evenly : 30 balanced permea~ility are obtained particularly when the thickness of the active layer in the subject cathodes is between about 0.05 and about 0.08 millimeters. Such active layers are so thin and fragile as to discourage handling thereof as separate layers or sheets in fabricating ., 9~
electrodes of practical sizes. Accordingly, a vital corollary factor in the practical realization OL durable oxygen cathodes for high energy density service in accordance with the present invention is the provision of a S sturdy, form-stable wetprooEing layer to which said unusually thin active layer is adhered.
This wet-proofing layer is electrically conductive and is usually substantiall~ thicker than said active layer.
In addition to the intimate mixtures of carbon black and tetrafluoroethylene binder particles used in its formation, it should be further strengthened by includin~ at least one anisometric reinforciny material therein and by heat sintering under pressure. Thus, said wetproofing la~er is preferably above about 0.1 millimeters in thickness. Also, the carbon black employed therein should have a particle size between 50 and about 3000 Angstroms and preferabl~
will be a highly conductive grade of carbon black such as an acet~lene black. Most acetylene blacks average between about 300 and about S00 Angstroms in size. The preferred particulate polymer for use therewith is polytetrafluoroethylene (commercially available from DuPont under the ~T~FLON" trademark). The anisometric reinforcing material can comprise short, chopped fibers of fine denier with L/D ratio of at least lOj and/or one or more layers of fine gauge mesh or gauze material. Particularly suitable are carbon or graphite fibers from about 1 to about 10 millimeters in length and about 5 to 100 micrometers in diameter, as well as mesh materials about S0 to about 200 micrometers thick, particularly closel~ woven metallic mesh materials which greatly improve current distribution in the finished electrode. For example, metallic meshes having between about 10 and about 20 individual wires per centimeter across both warp and fill directions are ideal.
The proportions in which the various components are ::, .
.
,:
9~
incorporated in the wetproofing la~er may be varied considerabl~ as long as a sturd~, form-stable electrically conductive layer is produced. Thus, the weight proportion of carbon black to tetrafluoroethylene binder particles should lie between about 3 to 2 and a~out 4 to 1, while the fibers used as reinforcement material should amount to between about 3% and about 25% of the combined weight of the carbon black and binder. ~einforcing mesn materials will usually constitute 10 to 25% by volume of the wetproofing layer. However, on a weight basis, the preferred electrically conductive metallic wire meshes may well account for over half of the total weignt of the wetproofing layer. ~etproofing layers acceptable for the needs of this invention have been disclosed in U.S. Patent . . _ . . .
4,468,362. If no mesh reinforcement is used, then the proportion of reinforcing fibers incorporated in the wet-proofing layer should be at least abc7ut 5~ of the combined weight of the carbon flack and binder.
Because of the inherent ~eakness of the unusually thin active layers per se, successful production of the finished oxygen cathode of this invention is reliably accomplisned by a unique but highly practical procedure wherein the sturdy, form-stable wetproofing layer is completely fabricated first ~including an embedded metallic mesh current distributor, if one is needed or desired therein), and, after heat sintering under pressure (e.g. 10 to 1000 psi), using said wetprooEing layer as a filter medium on which the composite particulates of which the active layer is to be formed are deposited from a well mixed dispersion in an alcoholic liquid by filtering same through said wetproofing layer. The alcoholic liquid emplo~ed to 7~
~,;i , , . , ~ .
~ ~ .
.:; .
~2~ 9~;
produce said dispersion should contain at least 50% by volume of a lower alkanol, prefera~ly one containiny not more than 6 carbon atoms per moleculeO Water or other fairly volatile, i~ert polar li~uids can be used as diluents in said alcoholic liquid. The amount of said dispersion filtered through ~aid wetproofing layer should be sufficient to deposit a coating of somewhere between about 2 and about ~ milligrams per square centimeter of geometric area on the face of said wetproofing layer, depending on the exact thickness desired for the active layer being formedO
once said coating oE active layer particulates nas been deposited on said wetprooeing layer, it is only necessary to dry same thoroughly under steady compression, preferably using temperatures somewhat above 100C and pressures of between about S00 and a~out 300U psi. It is not necessary, and generally is not preferred, to heat sinter the active layer.
Although not essential to the production of a fast response, high current density oxygen cathode with good durability, it is, of course, permissible and may be desirable if the extra expense is warranted, to apply to the exposed face of the active layer of said cathodes thin coatings of additional materials, such as catalysts and/or hydrophilic substances. One exemplary surEace tredtment of this type involved application of a very thin coating of silver particles to provide special catalytic effects in the presence of hydrogen peroxide containing electrolytes, as well as improving the resistance of the oxygen cathode to percol~tion of gas therethrough into the electrolyte.
It was found that a suitable coating of silver could be formed by depositing on the exposed face of said active layer about 5 to 15 milligrams of silver particles predominantly between about 0.1 and about 1 micrometer in ., ~- .
size per sq. cm. from a liquid dispersion thereof using a filtration procedure similar to that used in forming the+active layer upon the finished wet~roofing layer.
Generally speaking the thickness of such an auxiliary outer layer may be about 20 to about 50 micrometers, and preferably is thinner than the active layer of the electrode in ~uestion.
The specific examples wnich follow are provided to illustrate the the invention in more detail and to demonstrate some of the valuable advantages obtained therefrom.
EXAM~LE A
æreparation of Fiber Reinforced ~etproofing Layer A well mixed aqueous dispersion of 70 parts by weight of acetylene carbon black (SHA~INIGANTM Black) to 30 parts by weight of particulate polytetrafl~oroethylene (TE~LONT 30 dlspersion) was filtered in a Buchner funnel, and the wet solids were wasned thoroughly wit~
isopropyl alcohol. About 4.4 grams (dry basis) of the alcohol washed mixture of PTFE and acetylene black were then dispersed in about 3S0 ml of iso~ropyl alcohol along with 0.23 grams of one-eighth inch (0.032 cm) long carbon Eibers (P~NEXTM CF 30), using an OsterizerTM blender.
The mixed solids in this alcoholic dispersion were tnen formed into a uniform, mud-like layer by filtering enouyh of said dispersion to deposit about 18 milligrams (dry basis) of said solids per sq. cm. on a separable filter medium. The resulting damp layer of solids was dried at a~out 115 C while compressing same at S00 psi, before removing said filter medium. Finally, tne dry consolidated layer having a thickness of about 0.3 mm was heated to about 325C for a few minutes under 200 psi pressure in order to sinter the PTFE particles, thereby bondiny the mixed particulates together into a form-stable, electrically conductive web or sheetO
EXAr~lPLE E~
Fiber Reinforced Wetproofing Layer (with metal mesh embedded therein) Example A was repeated except that, before compressing and drying the damp layer of solids at aDout 115C and 500 psi, a coextensive layer of woven metal wire mesh ~as placed on top o said damp layer so that it became embedded in the resulting dry consolidated layer. Said metal mesa was made of silver plated, nickel coated copper wire o~
about 0.12 mm in diameter, (with about 20 individual wires per centimeter across both the warp and fill directions), and weighed approximately 40 milligrams per square cm.
EX~PLE C
~iber-Free Wetproofing Layer (with metal mesh embedded tnerein) Example B was repeated except no fibers were included : 30 in the alcoholic dispersion oE PTFE and acetylene black.
:: :
: : -..
; . ~ :.: .
.. . .
. . .
A ball milled and classified activated carbon having a ~.E.T. surface area of about llOOm2/g and about 60% by weight of which is in the ~article size ranye of about 2 to about 20 micrometers was impregnated with platinum b~
treatment with aqueous solutions of H3Pt(SO3)2O~ and H2O2 following a procedure much like that described in Example 1 of U.S. Patent 4,044,193, except that the proportions of reagents were adjusted to produce a catalyzed active carbon containing about 20~ platinum by weight. Tnis platinized active carbon was recovered by filtration, washing and drying at about 140C in air.
Twenty parts b~ weiyht of said platinized active carbon was thoroughly dispersed in about 300 ml of water using an Osterizerr~ blender and about an e~ual ~uantity of water containing enough "TE~LONTI~ 30 n to provide 5 parts by weight of PTFE was slowly blended therewith.
After the blended solids mixture was filtered out and washed with alcohol, it was redispersed in isopropanol to produce a suspension containing about 10 grams of the well mixed particles of platinized active carbon and PTFE per liter.
Varying amounts of this isopropanol suspension were 2S then filtered through four equal-sized square sections cut from the reinforced and heat sintered wetproofiny sneet made in EXAMPLE B hereinabove, said amounts being adjusted to coat said four sections with the following loadings of mixed particles from said suspension:
3~
B-l = 11.0 milligrams/cm2 B-2 = 3.4 milligrams/cm2 B-3 - 2.3 milliyrams/cm2 ~ B-4 = 1~7 milligrams/cm2 :. ".. ,.
, The resultant coated sections were then compressed at about 500 psi while heating to about 100C and finally pressed at about 3000 psi without Eurther heating to yield four finished electrode samples.
The durability of these sample electrodes for operation as oxygen cathodes in an environment simulating a metal-air batter~ was measured by the followiny standardized procedure.
The test cell was filled with 4 molar LiOH and provided with a chemicall~ inert nickel counter anoder a heater, a stirrer, a thermostat and a ~.C. po~er source.
On one side of said cell, a cathodic mount was provided to hold the sample electrodes directly facing toward said counter anode and including a separate gas compartment to the rear of said mount and a Luggin capillary for communicating between the test electrode and a standard Hg/~gO reference electrode, so that the half cell ~otential of the test electrode operating as an oxygen cathode could be tracked during the test.
The present series of tests was run at 25C using a current density of 500 milliamps per s~. cm. while circulating four times the theoretically needed ~uantity of air (puriEied of CO2) through the gas compartment behind the test electrode wi~h the following results.
SAMPLE ACTIVE LAYERTII~E OE STEADY OPE~ATION
ELECTRODETHICKNESS @500 ma/cm2 B-l 0.20 mm 10 minutes 30B-2 0.06 mm 6 hours B-3 0.04 mm 5 hours B-4 0.03 mm 3 hours , .,~
.
. . .
EXAMPL~ 2 Again using square sections cut from the reinforced wetproofing sheet of Example 3, a similar series of test electrodes were made as in Example 1 except that the active carbon was precatalyzed with cobalt tetramethoxyphenyl porphyrin in proportions of 1 part by weight of said porphyrin to 9 parts of active carbon, and then heat treated in N2 gas at about 800C for about 2 hours to produce the starting catalyzed active carbon component.
The sample electrodes were tested as oxygen cathodes as in Example 1 except at 60C, and tne results of tneir durability testing are summarized in the following table:
15 SAMPLE ACTI~ LAY~: STEADY OP~ATI~
ELECTRODæ SOLIDS LOADI~G THICK~S @$00 ma/cm2 ___ _~_________________________________ ___________________ B-5 6.6 9/crn 0.12 mm 1 hour ~-6 3.6 m9/cm~ 0.065 mm 6.5 hours B-7 3 3 mg/cm2 0.058 mm 11.5 hours Three isopropanol suspensions designated (X,Y and Z) were made as in ~xample 2, each containing the same proportions of PTFE and 10~ cobalt catalyzed active carbon particles and the only difference being that the starting active carbon particles were predominantly within much narrower size ranges. These suspensions were used to form active layer coatings each containing about 3.8 m9/cm2 of the solids mixture in said suspensions, using the filtration technique described in Examples 1 and 2 and additional s~uare sections of the same reinforced , 9~5 wetproofing sheet ~nade in ~xample B. The resulting coated sections o~ the wetproofing sheet were processed as in Example 1 to o~tain three additional test electrodes, each having an active layer thickness of about 0.07 mm. The results of testing these electrodes as oxyyen cathodes under the same conditions as in Example 2 were as follows:
SAMPLE P~E~OMINAI~T slr~A~y OP~ATIO
ELECTRODE SIZE RANGE @ 500 ma/cm2 ----______________________ B-X 2 and 10 m 7 hours B-Y 2 and 5 m 8 hours B-Z 5 and 10 m 19 hours The above illustrative examples are provided to give a more complete and detailed understanding of the practice oE
our invention and to point out presently preferred embodiments and some special advantages thereof.
Accordingly, those skilled in the art will now oe able to make various modifications in the specific conditions and employ other equivalent components to practice tnis invention, all of which variations are intended to be covered by the claims appended hereto.
~: :
:. :
:'
Claims (27)
1. A fast response, high current density oxygen cathode comprising: a form-stable, electrically conductive, wetproofing layer composed essentially of an intimate, consolidated and heat sintered mixture of carbon black and particulate hydrophobic polymeric binder derived predominantly from tetrafluoroethylene, having at least one anisometric electroconductive reinforcing material incor-porated therein; and, directly adhered to one surface of said wetproofing layer, a porous active layer having a thickness between about 0.03 and about 0.1 millimeter and composed essentially of a mixture of particles of a polymer of tetrafluorethylene and cobalt catalyst-containing particles of an active carbon predominantly of a size between about 2 and about 20 micrometers and having a Brunauer-Emmet-Teller surface area of over 1000m2/
gram.
gram.
2. An oxygen cathode as in claim 1 wherein said reinforcing material comprises at least one coextensive layer of fine mesh or gauze having a thickness of between about 50 and about 200 micrometers.
3. An oxygen cathode as in claim 1 wherein said reinforcing material comprises short, chopped fibers of fine denier.
4. An oxygen cathode as in claim 3 wherein said fibers are between about 1 and about 10 millimeters in length and about 5 to 100 micrometers in diameter.
5. An oxygen cathode as in claim 4 wherein said fibers are carbon or graphite.
6. An oxygen cathode as in claim 1 wherein said carbon black has a particle size between about 50 and about 3000 Angstroms.
7. An oxygen cathode as in claim 6 wherein said carbon black is an acetylene carbon black.
8. An oxygen cathode as in claim 1 wherein said catalyzed particles of active carbon contain between about 5% and about 25% by weight of a catalyst effective in promoting reduction of oxygen.
9. An oxygen cathode as in claim 8 wherein said catalyst is a macrocyclic organic compound of cobalt.
10. An oxygen cathode as in claim 9 wherein said catalyst is cobalt tetramethoxyphenylporphyrin which is heat treated after being deposited on said active carbon .
11. An oxygen cathode as in claim 1 wherein the thickness of said active layer is between about 50 and about 80 micrometers.
12. An oxygen cathode as in claim 1 wherein polytetrafluoroethylene is the predominant polymeric constituent in both the wetproofing and the active layers.
13. An oxygen cathode as in claim 1 wherein a light coating of submicron sized silver particles is pressed into the exposed face of said active layer.
14. An oxygen cathode as in claim 13 wherein said coating of silver particles is not more than about 50 micrometers thick.
15. An oxygen cathode as in claim 14 wherein said coating of silver particles is thinner than said active layer.
16. An oxygen cathode as in claim 1 wherein said active carbon particles are predominantly in the range between about 5 and about 10 micrometers.
17. An oxygen cathode as in claim 1 wherein said wetproofing layer is thicker than 0.1 millimeter.
18. An oxygen cathode as in claim 1 wherein said reinforcing material in fibrous and it accounts for between about 3% and about 25% of the combined weight of carbon black and binder and the weight proportion of carbon black to hydrophobic polymeric binder therein is between about 3 to 2 and about 4 to 1, while the weight proportion of catalyzed active carbon to polymer particles in said active layer is between about 7 to 3 and about 9 to 1.
19. An oxygen cathode as in claim 1 wherein said active layer is also heat sintered.
20. A method for preparing an oxygen cathode comprising:
(a) dispersing carbon black and particles of a hydrophobic polymeric binder in an alcoholic liquid, to form a well mixed particulate suspension;
(b) removing most of the alcoholic liquid from said suspension by filtering, centrifuging, evaporation or other liquid separation techniques to leave a mud-like, damp-solids mass of well mixed carbon black and hydrophobic binder particles;
(c) forming said damp-solids mass into a dry form-stable wetproofing layer by application of heat and pressure;
(d) heating the dry, form-stable wetproofing layer from step (c) to a temperature of at least about 325°C
while applying pressure thereto, thereby causing the hydrophobic binder particles to sinter and bond with other solid matter in said layer;
(e) forming a well mixed dispersion in alcoholic liquid of particles of a polymer of tetrafluoroethylene and precatalyzed particles of active carbon having a Brunauer-Emmet-Teller surface area of over about 1000 m2/gram and predominantly ranging between about 2 and about 20 micrometers in size;
(f) subjecting said well mixed dispersion from step (e) to filtration using the sintered form-stable wetproofing layer from step (d) as the filter medium to deposit over one face of said layer a thin coating of well mixed particles of said catalyzed active carbon and said polymer of polytetrafluoroethylene amounting to about 2 to about 6 milligrams of said well mixed particles per square centimeter of said face; and (g) drying said coating in place by application of heat and pressure, thereby forming said oxygen cathode having an active layer less than about 0.1 millimeter thick bonded to said form-stable wetproofing layer.
(a) dispersing carbon black and particles of a hydrophobic polymeric binder in an alcoholic liquid, to form a well mixed particulate suspension;
(b) removing most of the alcoholic liquid from said suspension by filtering, centrifuging, evaporation or other liquid separation techniques to leave a mud-like, damp-solids mass of well mixed carbon black and hydrophobic binder particles;
(c) forming said damp-solids mass into a dry form-stable wetproofing layer by application of heat and pressure;
(d) heating the dry, form-stable wetproofing layer from step (c) to a temperature of at least about 325°C
while applying pressure thereto, thereby causing the hydrophobic binder particles to sinter and bond with other solid matter in said layer;
(e) forming a well mixed dispersion in alcoholic liquid of particles of a polymer of tetrafluoroethylene and precatalyzed particles of active carbon having a Brunauer-Emmet-Teller surface area of over about 1000 m2/gram and predominantly ranging between about 2 and about 20 micrometers in size;
(f) subjecting said well mixed dispersion from step (e) to filtration using the sintered form-stable wetproofing layer from step (d) as the filter medium to deposit over one face of said layer a thin coating of well mixed particles of said catalyzed active carbon and said polymer of polytetrafluoroethylene amounting to about 2 to about 6 milligrams of said well mixed particles per square centimeter of said face; and (g) drying said coating in place by application of heat and pressure, thereby forming said oxygen cathode having an active layer less than about 0.1 millimeter thick bonded to said form-stable wetproofing layer.
21. A method as in claim 20 wherein a fine mesh, metal current distributor is incorporated into one face of the wetproofing layer formed in step (c) and the opposite face of said layer is the surface on which the thin coating is deposited during filtration step (f).
22. A method as in claim 20 wherein the composite, bonded-layer oxygen cathode formed in step (g) is heated to temperatures sufficient to effect some sintering of the tetrafluoroethylene polymer particles in said active layer.
23. A method as in claim 20 wherein the alcoholic liquid in step (a) contains at least 50% by volume of a lower alkanol.
24. A method as in claim 23 wherein said alkanol contains no more than 6 carbon atoms per molecule.
25. A method as in claim 20 wherein the weight proportion of carbon black to hydrophobic binder in step (a) is between about 3 to 2 and about 4 to 1, and the weight proportion of precatalyzed active carbon to tetrafluoroethylene polymer in step (e) is between about to 3 and about 9 to 1.
26. A method as in claim 20 wherein, after the completion of step (g), the resultant composite oxygen cathode is used as the filter medium in a filtration step wherein a liquid dispersion of silver particles predominantly in a size range between about 0.1 and about 1 micrometer is subjected to filtration on the exposed face of the active layer of said oxygen cathode, thereby depositing on said exposed face a thin coating of said silver particles at a loading of between about 5 and about 15 milligrams per square centimeter and consolidating said coating into an adherent, porous, surface layer of silver having a thickness of about 20 to about 50 micrometers.
27. A method as in claim 20 wherein at least 5% by weight of fine, short chopped fibers are included in step (a) based upon the total weight of solid matter in said particulate suspension.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/655,129 US4615954A (en) | 1984-09-27 | 1984-09-27 | Fast response, high rate, gas diffusion electrode and method of making same |
| US655,129 | 1984-09-27 |
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| Publication Number | Publication Date |
|---|---|
| CA1261915A true CA1261915A (en) | 1989-09-26 |
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| CA000489373A Expired CA1261915A (en) | 1984-09-27 | 1985-08-26 | Fast response, high rate, gas diffusion electrode and method of making same |
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| US (1) | US4615954A (en) |
| EP (1) | EP0176831B1 (en) |
| JP (1) | JPS6184387A (en) |
| AT (1) | ATE38588T1 (en) |
| BR (1) | BR8504629A (en) |
| CA (1) | CA1261915A (en) |
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| WO2012061817A1 (en) * | 2010-11-05 | 2012-05-10 | Florida State University Research Foundation, Inc. | Alkali metal-air flow batteries |
| JP6020896B2 (en) * | 2011-09-15 | 2016-11-02 | 日産自動車株式会社 | Assembled battery |
| US20150200082A1 (en) * | 2012-05-31 | 2015-07-16 | Ulvac, Inc. | Method of manufacturing metal hydroxides and method of manufacturing ito sputtering target |
| US9559374B2 (en) | 2012-07-27 | 2017-01-31 | Lockheed Martin Advanced Energy Storage, Llc | Electrochemical energy storage systems and methods featuring large negative half-cell potentials |
| JP2015018679A (en) * | 2013-07-10 | 2015-01-29 | 日本電信電話株式会社 | Lithium air secondary battery |
| DE102018205571A1 (en) * | 2018-03-29 | 2019-10-02 | Siemens Aktiengesellschaft | Gas diffusion electrode, an electrolysis device and a method for operating an electrolysis system |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3385780A (en) * | 1964-07-10 | 1968-05-28 | Exxon Research Engineering Co | Porous dual structure electrode |
| US3553022A (en) * | 1965-09-30 | 1971-01-05 | Leesona Corp | Electrochemical cell |
| US3462307A (en) * | 1966-04-28 | 1969-08-19 | American Cyanamid Co | Metal-air battery including fibrillated cathode |
| US3668014A (en) * | 1968-06-10 | 1972-06-06 | Leesona Corp | Electrode and method of producing same |
| GB1285199A (en) * | 1968-11-18 | 1972-08-09 | Westinghouse Electric Corp | Gas diffusion electrode |
| DE2208632C3 (en) * | 1972-02-24 | 1981-07-30 | Battelle-Institut E.V., 6000 Frankfurt | Process for the production of carbon-containing gas electrodes with a hydrophobic backing layer |
| NL7714464A (en) * | 1977-12-28 | 1979-07-02 | Electrochem Energieconversie | POROUS ELECTRODE. |
| NL7714575A (en) * | 1977-12-30 | 1979-07-03 | Shell Int Research | PROCEDURE FOR ACTIVATING A FUEL CELL ELECTRODES CATALYST. |
| US4255498A (en) * | 1979-10-26 | 1981-03-10 | Toshiba Ray-O-Vac Co., Ltd. | Button-type air cell |
| US4440617A (en) * | 1980-10-31 | 1984-04-03 | Diamond Shamrock Corporation | Non-bleeding electrode |
| US4468362A (en) * | 1980-10-31 | 1984-08-28 | Diamond Shamrock Corporation | Method of preparing an electrode backing layer |
| US4337139A (en) * | 1980-10-31 | 1982-06-29 | Diamond Shamrock Corporation | Fluorinated carbon electrode |
| US4456521A (en) * | 1980-10-31 | 1984-06-26 | Diamond Shamrock Corporation | Three layer laminate |
| KR830007884A (en) * | 1980-10-31 | 1983-11-07 | 앤 시이 헤릭크 | Matrix electrodes stacked in three layers |
| US4357262A (en) * | 1980-10-31 | 1982-11-02 | Diamond Shamrock Corporation | Electrode layer treating process |
| NL8006774A (en) * | 1980-12-13 | 1982-07-01 | Electrochem Energieconversie | FUEL CELL ELECTRODE AND METHOD FOR PRODUCING A FUEL CELL ELECTRODE |
-
1984
- 1984-09-27 US US06/655,129 patent/US4615954A/en not_active Expired - Fee Related
-
1985
- 1985-08-26 IL IL76196A patent/IL76196A/en unknown
- 1985-08-26 CA CA000489373A patent/CA1261915A/en not_active Expired
- 1985-09-12 AT AT85111533T patent/ATE38588T1/en not_active IP Right Cessation
- 1985-09-12 EP EP85111533A patent/EP0176831B1/en not_active Expired
- 1985-09-12 DE DE8585111533T patent/DE3566196D1/en not_active Expired
- 1985-09-20 BR BR8504629A patent/BR8504629A/en unknown
- 1985-09-27 JP JP60214377A patent/JPS6184387A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| ATE38588T1 (en) | 1988-11-15 |
| EP0176831B1 (en) | 1988-11-09 |
| JPS6184387A (en) | 1986-04-28 |
| DE3566196D1 (en) | 1988-12-15 |
| IL76196A0 (en) | 1985-12-31 |
| IL76196A (en) | 1988-08-31 |
| BR8504629A (en) | 1986-07-15 |
| EP0176831A2 (en) | 1986-04-09 |
| EP0176831A3 (en) | 1986-12-30 |
| US4615954A (en) | 1986-10-07 |
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